avcodec/flac_parser: Make expected_frame_num, expected_sample_num 64bit

Fixes: Integer overflow
Fixes: 17199/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FLAC_fuzzer-5696145187143680

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/flac_parser.c

@@ -313,7 +313,7 @@ static int check_header_mismatch(FLACParseContext  *fpc,
         (child_fi->frame_or_sample_num
          != header_fi->frame_or_sample_num + 1)) {
         FLACHeaderMarker *curr;
-        int expected_frame_num, expected_sample_num;
+        int64_t expected_frame_num, expected_sample_num;
         /* If there are frames in the middle we expect this deduction,
            as they are probably valid and this one follows it */